An anti-friction bearing is known comprising a bearing main body which is mounted for axial movement on a rail and has two end faces which are spaced in the axial direction of the rail and are substantially normal to the axis. The bearing main body has at least one pair of bearing member circuits, each one of which has a rectilinear, load-transmitting bearing member row in engagement with an axially parallel, load-absorbing track of the bearing main body. Each load-transmitting bearing member row is also in engagement with an axially parallel, load-absorbing track of the rail. Each bearing member circuit has a bearing member row running in the reverse direction and there are two curved bearing member rows between the latter and the respective load-transmitting bearing member row. The bearing member rows which run in the reverse direction are guided in the bearing main body by return channels approximately parallel to the axis. End plates are attached to the said end faces of the bearing main body, the end plates having deflection surfaces for curved bearing member rows. The end plates are made with axially parallel retaining webs which are located in alignment with one another and abut at their ends. The retaining webs secure the load-transmitting bearing member rows in engagement with the load-absorbing tracks of the bearing main body.
The known anti-friction bearings have cages (end plates and half webs) of plastics material. In the German Offenlegunggschrift No. 3,227,902 and in the German Offenlegungsschrift No. 3,148,331, there is described a bearing whose plastics cage is divided in two perpendicular to the axial plane. Each portion of the cage comprises an end plate having incorporated ball return recesses and five integrally molded retaining webs. The disadvantage of this construction, however, is the high number of retaining webs for the guidance of the four loaded ball rows since this construction requires a complicated and therefore uneconomical injection molding die and uses a great deal of material. In addition, larger radii or bevels are made on the bearing main body for the ball deflection at the exit or entry into the loaded ball raceways, which requires considerable re-machining. If this is not done, then shock-like loading and load relieving of the load-carrying balls results, together with an enormous edge pressure at the transition to the end plate. Therefore the cycle is impaired and the life of the bearing is considerably reduced. Moreover, despite the said radii, the cycle is not satisfactory in the embodiment according to the German Offenlegunggschrift No. 3,227,902, because the inner and outer deflection radii do not form concentric semi-circles, which leads to unsteadiness and varying ball play during deflection.
This shortcoming is largely removed in the construction disclosed in German Offenlegungsschrift No. 3,148,333. Here, however, the problem remains of continuing the outer radius in the bearing main body at the transition to the return bore. From the production point of view, this can only be done with great difficulty, if at all. To enable the linear bearing to be lubricated, remachining is likewise necessary by drilling a lubricating hole and several connecting channels in the bearing main body (German Offenlegungsschrift No. 3,227,902). This causes additional costs and increased time spent in the manufacture of the bearing element. Sealing is not provided. Consequently, the lubricant can escape very easily and dirt can penetrate into the bearing element, so that the life is reduced.
In another linear bearing disclosed in German Offenlegunggschrift No. 3,224,282, three additional strips to be screwed on in the bearing main body are added to four integrally molded cage retaining webs for two ball rows, which results in a further complication of the bearing unit. Furthermore, this construction suffers from the same disadvantages as those of German Offenlegungsschrift No. 3,227,902.
A ball sliding bearing having two plastics cage halves is known from the German Offenlegungsschrift No. 3,303,831. The construction disclosed in the latter, however, involves remachining the bearing main body and also involves the use of a complicated injection molding die so that the construction can produce the necessary deflection. Moreover, no subsequent lubrication and sealing is possible. In addition, the loading capacity of this bearing is limited, because the shaft cannot be continuously supported. Furthermore, the basis of this embodiment is not a bearing block which can be screwed directly over a flat contact surface, but a sleeve-like element which is located by a housing bore.
A cage for an open rail guide having two ball rows is described in French Patent Specification No. 2,523,669. The device can be made from metal or plastics and has features such as the cages described above. According to FIGS. 4 and 5 of French Patent Specification No. 2,523,669, the end plate and the ball guide for the two raceways of the two cage halves are in one piece. The balls are deflected in the end plate. Remachining is necessary to achieve a good transition and therefore a low wear and smooth cycle at the ball inlet and outlet. Nevertheless, it is not possible as above described in connection with the constructions of German Offenlegungsschrift No. 3,227,902 and German Offenlegungsschrift No. 3,148,333, to achieve any satisfactory cycle. Additionally, the manufacture of the end area "outer deflection radius", in conjunction with the return bore, produces considerable problems. Means of subsequent lubrication and seals are also lacking in this case.
However, bearing elements for longitudinal guides are also known in which considerable remachining of the loaded raceway ends of the bearing main body is no longer necessary and nevertheless a good ball transition and smooth ball running is achieved. In the constructions disclosed in German Offenlegungsschriften Nos. 3,005,579, 1,425,966, 3,313,129, 3,304,895 and 3,313,575, this is achieved by semi-cylindrical deflection pieces, the radius of which corresponds to half the ball diameter. The deflection pieces are inserted in recesses between the end plate and the end face of the bearing main body and therefore guide the balls from inside. The outer ball guidance is assumed by the known U-shaped recesses in the side plate. All these constructions have one common factor: the end plate, which provides for the ball deflection, and the retaining webs are made and assembled separately. Thus the number of parts is increased and therefore the production and assembly effort, as well as the number of joint transitions and sources of defects, are likewise increased.
The object of the invention is to provide an anti-friction bearing which can be easily manufactured especially in relation to the manufacture of the bearing main body, end plates and the retaining webs.